X-ray interferometer

ABSTRACT

Embodiments relate to an X-ray interferometer for imaging an object comprising: a phase grating for effecting in correspondence with the phase grating geometry a phase shift to at least a part of X-ray incident onto the phase grating; and an absorption grating for effecting in correspondence with the absorption grating geometry absorption to at least a part of X-ray incident onto the absorption grating. The grating period of the phase grating, and the grating period of the absorption grating may be dimensioned such that a detector for X-rays can be placed at a relatively large distance away from the absorption grating such the phase contrast sensitivity of the image of the object detected by the detector remains substantially unaffected.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit under 35 U.S.C. §119(a)-(d) ofSwiss Patent Application No. 1753/11 filed on Oct. 28, 2011, thedisclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Disclosed embodiments relate to imaging systems, and to X-ray imagingsystems, in particular.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the embodiments will become more clearlyunderstood in the light of the ensuing description of embodimentsthereof, given by way of example only, with reference to theaccompanying figures, wherein:

FIG. 1 is a schematic illustration of a setup of an X-rayinterferometer, in accordance with an embodiment;

FIG. 2A shows a reference image of an object acquired by employing asubstantially non-magnifying X-ray interferometer;

FIG. 2B shows a magnified image of the object acquired by employing anX-ray interferometer, in accordance with an embodiment;

FIG. 3A shows a visibility map of the reference image, in accordancewith an embodiment;

FIG. 3B shows a visibility map of the magnified image, in accordancewith an embodiment;

FIG. 4A schematically illustrates the phase contrast signal intensity atselected positions of the non-magnified image; and

FIG. 4B schematically illustrates the phase contrast signal intensity atthe same selected positions of the magnified image.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals and/or letters may be repeated among thefigures to indicate identical or analogous elements but may not bereferenced in the description for all figures.

DESCRIPTION OF THE RELATED ART

X-ray imaging is of high importance in view of its numerous applicationssuch as, for example, security screening, medical imaging, qualityinspection and non-destructive testing.

Conventional X-ray imaging is based on the detection of the material'sattenuation contrast of the object being imaged. There is growing needfor better resolution, accuracy, and improved frame rate of thegenerated X-ray image sequence. One method is X-ray phase contrastimaging which provides increased imaging contrast for weakly absorbingmaterials, as opposed to conventional X-ray imaging for which theobtained image contrast may be insufficient for practical applications.Weakly absorbing materials may include, for example, biological tissue,polymers or fiber composites.

The principle of X-ray phase contrast imaging is based on detectingminute changes in the direction of propagation, which are caused byrefraction of the X-rays passing through a phase shifting object.Equivalent to refraction in the visible light range, the change indirection is proportional to the local gradient in phase shift. Itshould however be noted, that the refractive power of matter for X-raysis many orders of magnitude weaker than for light in the visiblespectrum. Refraction of X-rays may cause a deflection angle in the orderof a few micro-radians. In X-ray phase contrast imaging it is thematerial's refraction index rather than the absorption coefficient whichis responsible for the image contrast.

X-ray phase contrast imaging may for example be based on the approachusing a Talbot-Lau or the Talbot grating interferometer. A Talbot-Lauinterferometer can be used to retrieve quantitative phase images withpolychromatic and incoherent X-ray sources, such as X-ray tube sources.The essential part of the interferometer includes two gratings placedbetween the object and the image detector. The first grating ispositioned upstream to the second grating with respect to the X-raysource. Consequently, the first grating is positioned between the secondgrating and the X-ray source, and the second grating is positionedbetween the image detector and the first grating. The phase grating isherein referred to as “phase grating”, and the second grating is hereinreferred to as “absorption grating”. It should however be noted that theterm “phase grating” should by no means to be construed as effectingonly a phase shift. Furthermore, the term “absorption grating” should byno means to be construed as only effecting absorption on incidentradiation. Correspondingly, the phase grating may, for example, absorbincident radiation, whilst the absorption may, for example, effect phaseshifting on incident radiation.

These gratings act as an array of collimating slits whose transmissionproperties strongly depend on the relative position of the two gratingsrelative to each other and the radiation angle of incidence on them.Since the angle of incident depends on the refractive powers exhibitedby the object on the incident radiation, any local phase gradient causedby the object causes a local change in intensity that may be recorded bythe detector.

X-ray phase contrast imaging using the principles of a Talbot-Lauinterferometry can thus employ state-of-the-art X-ray equipment such ashigh power X-ray tube sources and digital image sensors as detectors. Asa consequence, X-ray phase contrast imaging may be compatible with avariety of X-ray imaging applications such as scanning, tomography(e.g., Computer-Tomography) and radiography. Documents that related tointerferometry are discussed below.

Momose discloses in “Phase-sensitive imaging and phase tomography usingX-ray interferometers”, Optics Express, Vol. 11, No. 19, 22 Sep. 2003,that it is a characteristic of the Talbot effect that one can observethe appearance and disappearance of the image corresponding to thepattern of the grating along the optical axis. Talbot interferometryemploys two gratings. One grating (G2) is placed at a position where thepattern of the other grating (G1) is reproduced by the Talbot effect.Moiré fringes are generated by superposition if the two gratings areslightly inclined. The differential phase caused by an object placed infront of G1 is detected by moiré-fringe bending.

Pfeiffer, Weitkamp, Bunk and David disclose in “Phase retrieval anddifferential phase-contrast imaging with low-brilliance X-ray source”,Nature Physics, 26 Mar. 2006, doi: 10.1038/nphys265, that the totalexposure time of the detector can be greatly reduced by using a moreefficient detector, decreasing the distance between the source and theobject, and using standard rotating anode X-ray generators with a powerof a few kW.

European Patent application No. EP2060909 to Kottler et al., entitled“Interferometer device and method” discloses an interferometer devicecomprising an electromagnetic radiation source emitting radiation; aphase grating having a first aspect ratio; an absorption grating havinga second aspect ratio; and a detector. The electromagnetic radiationsource, the phase grating, the absorption grating and the detector areradiatively coupled with each other. The absorption grating ispositioned between the detector and the phase grating; theelectromagnetic radiation source is positioned in front of the sourcegrating; and the phase grating is designed such to cause on at least onewavelength of radiation passing through the grating bars a phase shift([Delta][Phi]) of less than [pi] relative to radiation passing betweenthe grating bars with respect to the at least one wavelength.

International patent application no. WO9849546 to J. F. Clauser,entitled “ultrahigh resolution interferometric x-ray imaging” disclosesa system that may operate in any of the following three modes:“geometric-shadow mode”, “amplitude-interferometric mode”, and“phase-interferometric mode”. The two interferometric modes, in turn,are each a multiplicity of discretely definable modes, andgeometric-shadow mode is a limiting case of one amplitude-inteferometricmode. Elimination of image blur by scatter is featured by all threemodes. Clauser discloses that the system also may employ any of threemethodologies—absorption contrast imaging, refractive-index gradientcontrast imaging, or element-selective contrast imaging. The choice ofmode depends to some extent on the choice of methodology and/or on thesystem's application. Geometric-shadow mode is used only for absorptioncontrast. Either of the interferometric modes gives refractive-indexcontrast, and/or element-selective contrast. Additionally, the systemcan employ more than two methodologies simultaneously, and can producetwo independent images simultaneously from a single x-ray exposure, e.g. one that shows only refractive-index-gradient contrast and one thatshows only absorption contrast.

J. C. Eliott and S. D. Dover disclose in “X-ray microtomography”,Journal of Microscopy 126, 211-213, 1982, a microscope system which isbased on the principles of computerized axial tomography for determiningthe distribution of the X-ray absorption coefficient in a slice from asolid object without cutting sections. Furthermore, an application isdisclosed to determine the distribution at a resolution of about 15 μmthrough a shell of about 0.5 mm diameter.

Engelhardt, Kottler, Bunk, David, Schroer, Baumann, Schuster andPfeiffer disclose in “The fractional Talbot effect in differential x-rayphase-contrast imaging for extended and polychromatic x-ray sources”simulations explaining why an interferometer could be combined withpolychromatic laboratory x-ray sources and that the distance between thephase and absorption grating of the interferometer is not generallylimited by the width of the photon energy spectrum.

Engelhardt, Baumann, Schuster, Kottler, Pfeiffer, Bunk and Daviddisclose in “High-resolution differential phase contrast imaging using amagnifying projection geometry with a microfocus x-ray source” inApplied Physics letter 90, 224101 (2007), that differential x-ray phasecontrast imaging using a grating interferometer in combination with amagnifying cone beam geometry using a conventional microfocus x-ray tubeeffects a magnifying cone beam setup.

Donath, Chabior, Pfeiffer, Bunk, Reznikova, Mohr, Hempel, Popescu,Hoheisel, Schuster, Baumann and David disclose in “Inverse geometry forgrating-based x-ray phase-contrast imaging”, Journal of Applied Physics106, 054703 (2009), a setup for CT applications, where the object ispositioned behind the phase grating.

In the above-mentioned phase contrast imaging methods and/or systems,magnification may be achieved by altering the position of the imagedobject further away from the phase grating, i.e., closer to the X-raysource. However, moving the object away from phase grating towards x-raysource may result in a decrease of phase contrast sensitivity attainableby the employed phase contrast imaging system and method.

The description above is presented as a general overview of related artin this field and should not be construed as an admission that any ofthe information it contains constitutes prior art against the presentpatent application.

DESCRIPTION OF EMBODIMENTS

One of the objects of the disclosed embodiments may be to provide anX-ray interferometer that is operative to image a object such that thetransverse or linear dimensions of the obtained image of the object areby multiplicative factor M higher than the lateral or linear dimensionsof the object itself, at least to a value meeting the constraintsimposed by the spatial resolvability of X-ray interferometer. In otherwords, the X-ray interferometer and imaging method may be operative toattain a multiplicative factor at least up to a value for which thespatial resolvability of the phase contrast imaging system is reached,i.e., two adjacent dots can still be rendered separately on the image.

Furthermore, according to embodiments, the X-ray interferometer may beoperative such that for any of the multiplicative value M, the requireddetection phase contrast sensitivity is not negatively affected, e.g.,for at least some practical X-ray imaging applications.

This object is achieved with an X-ray interferometer that comprises anX-ray source, a phase grating, an absorption grating and a detector. Thephase grating is positioned between the X-ray source, and the absorptiongrating is positioned between the phase grating and the detector. Thephase grating, the absorption grating and the detector are locateddownstream to the radiation direction of the X-ray source such that theyare optically coupled with each other, i.e., they are positioned inradially symmetrical alignment in respect of a mutually shared opticalaxis. An object to be imaged may be positioned between the X-ray sourceand the phase grating such that at least some of the radiation that canbe emitted by the X-ray source is incident onto the object.

According to embodiments, the detector is positioned at a distance fromthe absorption grating such to obtain a detectable or measurablemagnification of one or more portions of the imaged object. The detectormay thus for example be positioned at a distance from the absorptiongrating such that, on the one hand, magnification is obtained whilst theX-ray flux incident on the detector is still sufficient to be measurableby the detector. In addition, the distance between the detector and theabsorption grating may be chosen such that the magnified portion of theobject is still fully resolvable by the detector.

It follows from the above that the planar dimensions, perpendicular tothe optical axis, at least of the absorption grating may be smaller thanthe planar dimensions, also perpendicular to the optical axis, of thedetector's sensor field.

Otherwise stated, the magnitude of at least some of the imaginary linesdrawn between the geometric origin of the absorption grating to an edgepoint thereof, may be smaller than the magnitude of the parallel,imaginary line(s) respectively drawn between the geometric origin of thedetector to an edge point of the latter. The term “geometric origin” asused herein refers to the intersection point of the optical axis withthe corresponding optical element. Consequently, the absorption gratingmay only partially extend over the sensor field of the detector.Therefore, most or all of the X-ray radiation that may emanate from theabsorption grating may be incident onto the detector's sensor field. Inembodiments, the detector's sensor field scales with the multiplicativefactor M.

It suffices that the planar extensions of the absorption grating and/orof the detector may planarly extend or have lateral dimensionsperpendicular to the optical axis such to cover or extend over all ofthe object's cross-sectional planes that are also perpendicular to theoptical axis. However, these planar extensions do not need to cover thelateral extensions of the entire detector, which can be significantlylarger than the object size in order to be operative to render an imagerepresenting a magnification of the object. In embodiments, at leastmost or all of the X-ray radiation emanating from the object may beincident onto the phase grating and propagates towards the absorptiongrating, and at least most or all of the X-ray radiation emanating fromthe absorption grating may be incident onto the detector's sensor field.

A reduction in the required lateral dimension of the gratings may insome embodiments be advantageous in terms of their fabrication becausethe larger the grating, the more difficult it is to obtain homogeneousdiffraction characteristics. Moreover, the handling, manipulation andalignment of smaller gratings are less demanding than with comparablylarger area gratings. In view of the aforesaid, the costs for the X-rayinterferometer according to embodiments may be comparably reduced.

Considering for example that the object size extends in the x-directionand y-direction to a few centimetres like, e.g. about 20 cm, thecorresponding lateral dimensions of the absorption grating may thusplanarly extend from, e.g., about at least 20 cm to, e.g., up to about25 cm. To remove any semblance of doubt, it should be noted that theterm “emanating radiation”, as well as grammatical variations thereofmay also relate to or include radiation diffracted and/or refracted froman X-ray source. Therefore, depending on the desired multiplicativefactor M of a portion of the object, the required maximal width of theabsorption grating may be smaller than the maximal width of the detectorby a factor of, for example, about at least 1.5, about at least 2, aboutat least 2.5, about at least 3, or about at least 10.

Thus, according to embodiments of the invention, phase contrast imagesmay be obtained that provide a magnified image of at least a portion ofthe imaged object, wherein the information shown by the magnified imagemay be resolvable by the detector, whilst the X-ray flux incident ontothe detector may remain substantially unchanged or even increase.Furthermore, the planar extensions of the absorption grating may besmaller than the planar extensions of the detector down to the planarextensions of the object in the x-y plane. A decrease in the planarextensions of the absorption grating correspondingly may reduce therequired investment in materials and manufacturing time. Moreover, thecomplexity of the production facility for the manufacturing of theabsorption may be reduced.

Objects that may be imaged by the X-ray interferometer in accordancewith embodiments may include, for example, any type of specimen,biological tissue (e.g., skin tissue, muscle tissue, vascular tissue,organ tissue, cancerous tissue), polymers, fibre composites, or anyother material or composition of materials having, e.g., a density thatis lower than that of osseous tissue of Vertebrates, e.g., having adensity being about equal or less than about 1.56 g/cm³, less than about1.25 g/cm³, less than about 1.15 g/cm³, less than about 1.06 g/cm³, lessthan about 1 g/cm³, less than about 0.9 g/cm³, or less than about 0.85g/cm³. It should be noted that the latter statement relating to densityshould by no means to be construed as limiting. The X-ray interferometermay additionally or alternatively also be operative to image objectshaving a density that may be equal or higher than that of osseous tissueof Vertebrates. Correspondingly, the X-ray interferometer may beoperative to image tissue having a density that is higher than about1.56 g/cm³.

The X-ray interferometer may be employed in various applications, forexample, in Computer-Tomography (CT) for three-dimensional visualizationinside objects with resolutions down to the micrometer range or evenbelow. Applications include, for example, medical and/or industrialapplications and/or any other application that may require imaging ofcross-sectional planes or slices of object. Medical applications mayinclude, for example, mammography. Industrial applications may relate,for example, to non-destructive testing of material.

SUMMARY OF EMBODIMENTS

Embodiments are related to an X-ray interferometer for imaging an objectby irradiating the object with X-rays emitted, e.g., by a point X-raysource at a given radiation energy. The X-ray interferometer comprises aphase grating for effecting in correspondence with the phase gratinggeometry a phase shift to at least a part of X-ray incident onto thephase grating; and an absorption grating for effecting in correspondencewith the absorption grating geometry absorption to at least a part ofX-ray incident onto the absorption grating.

In embodiments, the grating period of the phase grating and/or of thegrating period of the absorption grating are dimensioned such that anX-ray detector for imaging the object can be placed at a relativelylarge distance away from the absorption grating such that for the givenradiation energy, the X-ray flux incident onto the detector issubstantially non-adversely affected.

In embodiments, the X-ray interferometer further includes the detectorfor X-rays placed at a relatively large distance away from theabsorption grating.

In embodiments, the distance is selected such to allow a detectabledivergence of or effect a corresponding image magnification by thephase- and intensity-modulated X-ray emanating from the absorptiongrating and incident onto the detector.

In embodiments, the X-ray interferometer is a Talbot or Talbot-LauInterferometer.

In embodiments, the grating periods of the phase grating and of theabsorption grating are dimensioned such the detector can be placed at arelatively large distance away from the absorption grating such that forthe given radiation energy the phase contrast sensitivity of the imageof the object detectable by the detector is substantially non-adverselyaffected, (e.g., remains substantially the same or may even increase).

In embodiments, respective of a given radiation energy, the gratingperiods of the absorption grating and the phase grating are dimensionedsuch that placing the detector at relatively large distance from theabsorption grating results in a corresponding increase in the attainableimage magnification of an object to be imaged while at the same time thephase contrast sensitivity of an image of the object detectable by thedetector and/or the X-ray flux incident on the detector is substantiallynon-adversely affected (i.e., remains substantially the same or may evenincrease).

In embodiments, the grating periods of the phase grating and of theabsorption grating are dimensioned such that the phase contrastsensitivity of the image of the object detected by the detector of theX-ray interferometer is substantially not adversely affected by placingthe detector at a relatively large distance away from the absorptiongrating.

In embodiments, the lateral extensions of the phase grating, theabsorption grating and the detector cover the diverging field sizerespective of the X-ray emanating from the object when being imaged.

In embodiments, during imaging, the grating periods of the phase andabsorption grating can be dimensioned or selected such that the distancebetween the object and the phase grating can be selected tosubstantially equal zero.

In embodiments, the phase contrast sensitivity of an image of the objectremains substantially equal or increases, compared to the phase contrastsensitivity of an image of at least a part of the object when thedistance between the detector and the absorption grating substantiallyequals 0.

In embodiments, the lateral dimensions of the phase grating, theabsorption grating and the detector are such to allow for selecting thedistance between the detector and the absorption grating to obtain acorresponding change in the multiplicative factor between the lateraldimensions of the image and the object itself.

In embodiments, the phase contrast sensitivity of the image ranges fromabout 150 to about at least 300.

In embodiments, wherein the obtainable magnification ranges from greaterthan 1 to about at least 50.

Embodiments relate to a method for performing phase contrast imaging byemploying an X-ray interferometer. In embodiments, the method comprisesdimensioning the grating period of the phase grating and of theabsorption grating such that a detector can be placed at a relativelylarge distance away from the absorption grating, in a manner allowing adetectable divergence of the phase- and intensity-modulated X-ray fromthe absorption grating to the detector, and such that for the givenenergy, the X-ray flux incident onto the detector during imaging issubstantially non-adversely affected.

In embodiments, the method comprises positioning the object at distancefrom the phase grating which substantially equals zero.

DESCRIPTION OF EMBODIMENTS

Embodiments relate to providing an X-ray interferometer that enablesproviding an image of an object, wherein the lateral dimensions of theimage are by a multiplicative factor higher than the lateral dimensionsof the object to be imaged.

It should be noted that the term “coherent” and “monochromatic” as usedherein as well as grammatical variations thereof also may also encompassthe meaning of the term “substantially coherent” and “substantiallymonochromatic”, respectively.

In many fields of potential applications such as in industry or medicinehigher X-ray energies are demanded in order to provide sufficient objecttransmission. Therefore, by enabling interferometry with, e.g., X-raysemitted from the X-ray source at mean energies of, for example, about atleast 20 keV, about at least 40 keV, about at least 60 keV, or about atleast 80 keV, the type of materials and objects that can be imagedenabling practical applications is largely increased.

It should be noted that the adjective “equal” as used herein may alsoencompass the adjective “substantially equal”.

It should be noted that although the embodiments are described hereinand exemplified with reference to an X-ray interferometer that is basedon the principles of a Talbot-interferometer, this should by no means tobe construed as limiting. Consequently, embodiments may likewise beimplemented based on the principles of, e.g., a Talbot-Lauinterferometer. Consequently, in accordance with an embodiment, theX-ray interferometer may include three gratings, e.g., as known in theart. In some embodiments, the X-ray interferometer may optionallyinclude a source grating, which may be positioned between radiationsource and phase grating. An object to be imaged may be positionedbetween source grating and phase grating. Source grating may beoperative, for example, to cause radiation emitted by X-ray source tobecome spatially coherent. The X-ray interferometer may thus embody aTalbot-Lau interferometer.

It should be noted that the term “spatially coherent”, as well asgrammatical variations thereof, may also encompass the meaning of theterm “substantially spatially coherent” or “at least approximatelyspatially coherent”.

Reference is now made to FIG. 1, which is a schematic illustration of anX-ray interferometer 100, in accordance with an embodiment.

X-ray interferometer 100 may include, for example, an X-ray source 110,a phase grating 122, an absorption grating 123, and a detector 140 thatis operative to detect radiation emitted by X-ray source 110.

Phase grating 122 is positioned between X-ray source 110 and absorptiongrating 123, and absorption grating 123 is positioned between phasegrating 122 and detector 140. Phase grating 122 may be manufactured froma phase shifting and substantially non-absorbing material for X-ray suchas, for example, silicon. Absorption grating 123 may be made from anX-ray absorbing material such as, for example, gold.

X-ray source 110, phase grating 122, absorption grating 123 and 140 areoptically coupled with each other such that radiation emanating fromX-ray source 110 is incident onto phase grating 122, absorption grating123 and detector 140 allowing the imaging of an object 130, which may bepositioned between X-ray source 110 and phase grating 123. In otherwords, X-ray source 110 is operative to emit radiation which may beincident onto phase grating 122 and result in radiation that furtherpropagates from phase grating 122 and is incident onto absorptiongrating 123. The radiation incident onto absorption grating 123 maysubsequently result in radiation that emanates from absorption grating123 and is incident onto detector 140.

Consequently, if the radiation emitted by X-ray source 110 is responsiveto at least some differences in the material of object 130 as welltransmissive to the emitted radiation, such differences may be recordedby detector 140, as outlined herein below in greater detail.

X-ray source 110 may be embodied, for example, by an electromagnetic(EM) radiation source that is operative to emit a radiation beam havingconical divergence geometry. As a result, X-ray source 110 may providethe effect of a projection magnification M, which can for example bedefined as follows:

$\begin{matrix}{M = \frac{R^{\prime}}{R}} & (1)\end{matrix}$

wherein R—denotes the object size of object 130, and R′ denotes the sizeof the image of object 130 projected onto detector 140. In accordancewith embodiments, magnification M is higher than 1 and may range, forexample, from 1, from about 1.1, or from about 1.5 to about at least 50.

It should be noted that the term “conical” as used herein, as well asgrammatical variations thereof, may also encompass the meaning of theterm “substantially conical” or “at least approximately conical”.Furthermore, the term “point source” as used herein, as well asgrammatical variations thereof, may also encompass the meaning of theterm “substantially a point source” or “at least approximately a pointsource”.

X-ray source 110 may be embodied, for example, by a point source ofradiation such as, for example, a micro-focus X-ray source, e.g., asknown in the art. X-ray source 110 may have an output of a W target andbe operative to emit light having a focal spot size ranging, forexample, from about 0.1 to about at least 3000 μm, when operated at tubevoltage of, e.g., 20 to 170 kV and at a tube current of, e.g., about 0.1μA to about at least 50,000 μA. The X-ray beam angle, measured at thesource, may range, for example, from about 35 to about at least 120degrees.

Grating period of phase grating 122 and absorption grating 123 areherein denoted as P₁₂₂ and P₁₂₃, respectively.

λ—denotes the wavelength of the X-ray emitted by X-ray source 110.

n—denotes the fractional Talbot order

η—denotes the symmetry parameter

M—denotes the multiplicative factor of the image of an object byemploying X-ray interferometer 100.

I—denotes the distance between X-ray source 110 and phase grating 122

d—denotes the distance between phase grating 122 and absorption grating123;

d_(M)—denotes the distance between absorption grating 123 and detector140,

Q—denotes the maximal distance between phase grating 122 and object 130(which may be limited by X-ray source 110 or a source grating (notshown)), and

d_(s)—denotes the distance between plane 115 which is perpendicular tothe optical axis Z and which intersects with the geometric centre ofobject 130. The said plane 115 is hereinafter referred to as “centreplane” 115.

For the discussion that follows, it is assumed that the widths of phasegrating 122 and absorption grating 123 is infinitely small or at leastnegligible with respect to the distances I, d and d_(M). It may furtherbe assumed, that the position of object 130 is such that the distancebetween centre plane 115 and phase grating 122 is infinitely small or atleast negligible compared to the distances I, d and d_(M). It is beassumed that the distance d is small compared to the distances I andd_(M), i.e., d<<d_(M) and d<<I. However, the above-outlined assumptionsshould not be construed as limiting and are thus not a precondition forthe operability of X-ray interferometer 100 as outlined herein.

To enable phase contrast imaging of object 130 with X-ray interferometer100, the following three constraints may have to be met:

$\begin{matrix}{D_{n} = {n \cdot \frac{p_{1}^{2}}{8\; \lambda}}} & (2)\end{matrix}$

wherein D_(n) denotes the fractional Talbot distance

$\begin{matrix}{d_{n} = \frac{l \cdot D_{n}}{l - D_{n}}} & (3)\end{matrix}$

wherein d_(n) denotes the Talbot distance which is corrected fordivergence; and

$\begin{matrix}{\frac{\eta \cdot p_{2}}{p_{1}} = \frac{l + d}{l}} & (4)\end{matrix}$

which defines the condition for beam divergence.

Following equations 1, 2 and 3, the distances I and d can, for example,be parameterised by the X-ray wavelength A, e.g., as follows:

$\begin{matrix}{d = \frac{n \cdot \eta \cdot p_{1} \cdot p_{2}}{8 \cdot \lambda}} & (5) \\{l = {d \cdot \frac{p_{1}}{{\eta \cdot p_{2}} - p_{1}}}} & (6)\end{matrix}$

It should be noted that other mathematical terms those outlined hereinmay be used to express the same physical conditions.

The parameter ρ in these equations reflects the symmetry of theinterference pattern between the wavefronts emanating from absorptiongrating 123. The symmetry depends on the design of phase grating 122, asoutlined herein below. In case phase grating 122 is designed such thatit shifts incident wavefront by, e.g., ΔΦ=π then η=2. In case phasegrating 122 is designed such that ΔΦ<π (for example π/2), then η=1.According to these equations, for given grating periods P₁₂₂ and P₁₂₃ ofphase grating 122 and absorption grating 123, respectively, theparameters I and d and therefore the overall distance between X-raysource 110 and detector 140 may have to increase, linearly, withincreasing X-ray energy emitted by X-ray source 110, to meet theconstraints expressed in equations 1) to 3).

According to some embodiments, multiplicative factor M that may beeffected by X-ray interferometer 100 may be expressed by the followingmathematical term:

$\begin{matrix}\begin{matrix}{M = \frac{R^{\prime}}{R}} \\{= \frac{d_{M} + d + l}{l - d_{S}}}\end{matrix} & (7)\end{matrix}$

According to embodiments, X-ray interferometer 100 may be operative suchthat the ratio M, which is also the multiplicative factor, of the sizeof the image of object 130 on detector 140 to the size of the imagedobject 130 is at least M>1. For example, altering the distance d_(M)results in a corresponding change in the multiplicative factor M.Altering d_(M1) to d_(M2), wherein d_(M2)>d_(M1), results in an increaseof the multiplicative factor M and therefore in a lateral magnification.Conversely, altering d_(M2) to d_(M1), results in a decrease in of themultiplicative factor M and therefore in a reduction of the lateralscale of the image or minification. In other words, magnification isachieved at least by positioning detector 140 away from absorptiongrating 123 and farther downstream of X-ray propagation beam path.Consequently, detector 140 may be physically decoupled from absorptiongrating 123.

According to embodiments, X-ray interferometer 100 may be operative suchthat by altering d_(M) a corresponding change in the multiplicativefactor M may be obtained even if the distance d_(s) remains unchanged.Considering, for example, d_(s) has any value between 0 to Q, a changeof d_(M) from d_(M1) to d_(M2), wherein d_(M2)>d_(M1) results in anincrease of the multiplicative factor M, which is reflected by an imagerepresenting a magnification of object 130.

Additionally or alternatively, a change in the multiplicative factor Mmay be obtained by altering d_(s), i.e., by changing the distance ofobject 130 relative to phase grating 122. For example, when alteringd_(s) from d_(s1) to d_(s2), wherein d_(s1)<d_(s2), may result in anincrease in the multiplicative factor, and vice versa.

In some embodiments, d_(M) may be selected up until the maximum valuefor which X-ray interferometer 100 is operative to render two dotsseparately on an image of object 130, i.e., magnification M attains avalue which is below what is sometimes dubbed “empty magnification”.

Phase Contrast or Angular Sensitivity [rad^(−1]:)

The phase shift {umlaut over (ο)} (x,y) imposed on the wave field byobject 130 positioned in the beam path causes a refraction of the beamin x-direction by the angle á, which is connected with the differentialphase shift ∂Φ/∂xby

$\begin{matrix}{\alpha = {\frac{\lambda}{2\; \pi}\frac{\partial\Phi}{\partial x}}} & (8)\end{matrix}$

with the X-ray wavelength λ and the beam propagation along thez-direction. The term “phase contrast or angular sensitivity” (S) asused herein may be defined as the ratio of phase-shift Äö in theintensity oscillation of the phase scan (normalized to 2ò) to therefraction angle a caused by object 130:

$\begin{matrix}{S \equiv {\frac{1}{2\; \pi}\frac{\Delta \; \phi}{\alpha}}} & (9)\end{matrix}$

The measurement of phase contrast sensitivity depends, at leastpartially, on the relative position of object 130 with respect to phasegrating 122 and absorption grating 123 and increases the closer object130 is put behind phase grating 122, and vice versa.

In some embodiments, the position of object 130 may thus be chosen to atleast partially compensate for any reduction in the phase contrastsensitivity of X-ray interferometer 100 that may otherwise occur due tochoosing d_(M2) instead of d_(M1), wherein d_(M2)>d_(M1). For example,object 130 may be placed before phase grating 123 in a manner preventingnegatively affecting the phase contrast sensitivity that may occur dueto alteration the position of object 130 from d_(M1) to d_(M2).

At least partial compensation for possible reduction of phase contrastsensitivity may for example be achieved by correspondingly placingobject 130 closer to phase grating 122, i.e., by altering d_(s) fromd_(s1) to d_(s2), wherein d_(s2)<d_(s1). Additionally or alternatively,orientation of object 130 may be chosen such that for a distance d_(si)the average distance of all points of object 130 to phase grating 122 isat least approximately minimized.

At some instances, the phase contrast sensitivity for d_(M)>1 for X-rayinterferometer 100 as opposed to d_(M)=0 in substantiallynon-multiplicative or substantially non-magnifying X-ray interferometersmay even increase. X-ray interferometer 100 may for example beconfigured such to be operative to obtain an image of object 130 with aphase contrast sensitivity ranging, for example, from about 25 to aboutat least 260. For example, the phase contrast sensitivity attainable byX-ray interferometer 100 may be, for example, about at least 25, aboutat least 50, about at least 120, about at least 160, about at least 200or about at least 260.

Assuming now, for example, d_(s)=0; or d_(s)≈0; or d_(s)<<d_(M),d_(s)<<d and d_(s)<<I, equation 6 can then be approximated as follows:

$\begin{matrix}\begin{matrix}{M = {\frac{R^{\prime}}{R} \approx {1 + \frac{d_{M}}{l}}}} \\{= \frac{l + d_{M}}{l}}\end{matrix} & (10)\end{matrix}$

Consequently, the degree of magnification can be selectively adjustedwithout necessarily having to change the parameters of phase grating 122and absorption grating 123. Otherwise stated, if d_(s)=0; or d_(s)≈0; ord_(s)<<d_(M) and d_(s)<<d and d_(s)<<I, then for any d_(M)>0 theobtainable phase contrast sensitivity is at least approximately orsubstantially maximized compared to when ds<d_(M), and a correspondingmultiplication factor of M>1 enabling practical imaging applications(e.g., M≧2, ≧3, ≧5, or, e.g., M≧10) may be obtainable with X-rayinterferometer 100 without necessarily having to compromise on phasesensitivity. Correspondingly, the phase contrast sensitivity may attaina value which is at least approximately equal to the maximal phasecontrast sensitivity that may theoretically be obtainable by X-rayinterferometer 100 in case object 130 had, theoretically, infinitelysmall width (measured along optical Z-axis).

Spatial Resolution

The achievable spatial resolvability by interferometer system 100 whenimaging object 130 is determined, for example, by the spatial resolutionof detector 140 and the focal spot size of X-ray source 110.Furthermore, the achievable spatial resolvability may be limited by thegrating period of, e.g., phase grating 122. Once the wave frontoriginating from X-ray source 110 has passed phase grating 122, theinformation on the local deflection effected on the wavefront by phasegrating 122 is limited by or can not be resolved beyond the gratingperiod P₁₂₂. Thus, a reduced grating period P₁₂₂ may allow for greaterspatial resolvability of the imaged object 130 by interferometer 100,and vice versa. More specifically, attainable magnification M may berestricted to a value for which the spatial resolution in the imageplane (not shown) of phase grating 122 is larger than grating periodP₁₂₂ of phase grating 122. The achievable spatial resolvability of twoadjacent dots may thus be, for example, about 3 μm or less.

Considering distance X as the spatial resolution of detector 140 (forexample, the distance between two adjacent pixels) leads to thefollowing condition: M>X/P₁₂₂, i.e., consequence, grating period P₁₂₂must be smaller than X to be able to attain M>1. As a ence if object 130is positioned as close as possible to phase grating 122 such that d_(s)equals or at least approximately equals 0, the spatial resolution islimited to the phase grating period P₁₂₂. If d_(s)>>0, the limitation ofspatial resolvability by phase grating 122 is given by theback-projected period of P₁₂₂ onto object 130. The back projected periodis hereinafter referred to as “P_(back-122)”. P_(back-122) can besmaller than the grating period P₁₂₂ and can be expressed, for example,as follows:

P _(back-122) =P ₁₂₂·((l−d _(s))Il)

Therefore, if the application calls for a spatial resolution that isbetter than (i.e. below that of) grating period P₁₂₂, the spatialresolution can be improved by moving object 130 away from phase grating122 (d_(s)>0). However, increasing d_(s) will be at the expense of theattainable phase contrast sensitivity. The optimal configuration ofphase contrast imaging system 100 is thus determined by the specificoperation requirement for a particular imaging application.

Spatial Coherence:

The requirement on sufficient spatial coherence for phase contrastimaging system 100 may have to be met. In general, these requirementsare fulfilled because the focal spot size of X-ray tube sourcestypically used in micro CT may be such to be substantially compatiblewith coherence requirements for practical applications. The focal spotsize may for example range from about 0.1 μm to about at least 3000 μm,or range from about 0.1 μm to about at least 50 μm. Furthermore, themagnitude of grating periods P₁₂₂ and P₁₂₃ may range, for example, fromabout 0.05 μm, about 1 μm, or about 1 μm to, e.g., about 10 mm orhigher.

Distance d_(M) between absorption grating 123 and detector 140 isgreater than 0 cm and can be up to a few meters such as, for example,about at least 1 mm, about at least 2 mm, about at least 1 cm, about atleast 2 cm, about at least 3 cm, about at least 5 cm, about at least 6cm, about at least 7 cm, about at least 8 cm, about at least 9 cm, aboutat least 10 cm, about at least 15 cm, about at least 20 cm, about atleast 50 cm, about at least 1 m, about at least 1.5 m or about at least2 m. In some embodiments, X-ray interferometer 100 may be configuredsuch that the position of detector 140 and/or absorption grating 123 aremoveable relative to each other enabling selectively setting distanced_(M) in a manner such that imaging parameters (e.g., phase contrastsensitivity and/or spatial resolution) for an object 130 to be imagedare met. In some embodiments X-ray interferometer 100 may, for example,include a support (not shown) on which detector 140 and/or absorptiongrating 123 may be mounted for enabling selectively setting, discretelyor slidably, distance d_(M).

Additional reference is now made to FIG. 2A which illustrates areference image of object 130 acquired by substantially non-magnifyingX-ray interferometer; to FIG. 2B, which illustrates a magnified image ofobject 130 acquired by X-ray interferometer 100, in accordance with anembodiment; to FIG. 3A, which illustrates a visibility map of thereference image, in accordance with an embodiment; and to FIG. 3B, whichillustrates a visibility of the magnified image, in accordance with anembodiment.

Visibility of a Selected Area/Region of Interest of an Image as a Figureof Merit for the Performance of X-ray Interferometer 100:

With respect to phase contrast imaging, the visibility of an image ofobject 130 may for example be defined as the relative height between themaximum and minimum intensity of the interference fringes. Accordingly,the measured visibility can be a figure of merit for the performance ofthe respective X-ray interferometer.

Various techniques may be applied for determining visibility. Forexample, a phase-stepping procedure may be employed, wherein thevisibility can be determined pixel-wise and a map of the visibility overthe entire field of view can be obtained. Defects of the gratings causespecific spots of poor visibility on these maps. Such spots, referenced250, can be identified in the visibility maps shown in FIGS. 3A and 3B.

The quality of the employed gratings determines the visibilityattainable by X-ray interferometer 100. The mean value of the visibilityover a region of interest of an image may thus be a representativemeasure for the visibility of the entire image generated by X-rayinterferometer 100. The reason therefor is as follows: a wave fielddownstream of absorption grating 123 continues propagating and forms afirst interference pattern at a first period. However, the intensitymeasured at the pixel of detector 140 is independent of a particularfringe pattern, since detector 140 measures the average intensity overmany periods of the fringes. This is true for any M>0 up to a value forwhich an increased number of details are made visible on the obtainedmagnified image.

Influence of d_(M) on Visibility

X-ray interferometer 100 may, in some embodiments, be operative suchthat the visibility is substantially independent or unaffected by anincrease or decrease of the distance denoted d_(M) between absorptiongrating 123 and detector 140. In other words, the influence on thevisibility by increasing or decreasing d_(M) is comparably negligible,as outlined herein below in greater detail. In particular, settingd_(m)>0 (e.g., to a distance of, for example, 1 mm to 3 m) as opposed towhere d_(M) substantially equals 0, has a negligible effect on thevisibility of the phase contrast images obtainable with X-rayinterferometer 100.

Both the substantially non-magnifying X-ray interferometer as well asX-ray interferometer 100 which were respectively employed for generatingthe images shown in FIGS. 2A and 2B, are based on the Talbot-Lauinterferometer principle. However, as already mentioned herein above,this should by no means to be construed as limiting. To implement theTalbot-Lau based interferometer, both the substantially non-magnifyingX-ray interferometer as well as X-ray interferometer 100 employ X-raysource 110 which is assumed to have the appropriate focal spot size.Furthermore, detector 140 of X-ray interferometer 100 is operative toprovide sufficient spatial resolution so that the multiplicative factorM may only be limited by the grating period P₁₂₂.

In the examples shown, phase contrast images were acquired for object130 that is embodied by three rods, each one being made of a differentmaterial of plastic. The diameters of each one of the three rods measureabout 6 mm. Both images show the same region of interest of the sensorfield of detector 140.

A region of interest (ROI) 201A of a non-magnified image 200A of object130 is magnified by X-ray interferometer 100 which results in amagnified image 200B.

ROI 202A schematically outlines a specific region of non-magnified image200A for which the visibility is determined. Correspondingly, ROI 202Bschematically outlines the boundary of the region of interest ofmagnified image 200B for which average visibility is determined.

In both images 200A and 200B identical areas of field of views ofdetector 140 are displayed. Further parameters of the imaging setup wereas follows: I equals about 126 cm, d equals about 19.0 cm, P₁₂₂ equalsabout 2.6 μm, and p₁₂₃ equals about 3.0 μm. The focal spot size of X-raysource 110 was about 1 mm. Clearly, second phase contrast image 200Bwhich is taken with d_(M) equalling about 70 cm shows the rods magnifiedcompared to the case where d_(M) equals about 0. The attainedmagnification M equals about 1.48 with respect to the image at d_(M)equals about 0.

Visibility measurements were performed with the Talbot-Lauinterferometer, because an X-ray tube source with a focal spot size ofabout 1 mm² was used. The source grating that was used had a gratingperiod of equals about 20 μm. Because of the size of the focal spot thespatial resolution may not improve. However, the effect of the distanced_(M) on the visibility can be analysed appropriately. For the caseexemplified hereinabove, the visibility of ROI 205A and ROI 205B equalsabout 0.205 and equals about 0.214, respectively. Thus, second phasecontrast image 200B maintains approximately the same visibility valuedespite magnification of M>1.3.

Further reference is made to FIG. 4A, which schematically illustratesthe phase contrast signal intensity at selected positions ofnon-magnified image 200A; and to FIG. 4B which schematically illustratesthe phase contrast signal intensity at the same selected positions ofmagnified image 200B.

The phase contrast signal intensity may for example be determined for aparticular row of matrix image data and for all column values. Such aselection of image data is schematically illustrated with dashed lines204A and 204B, both of which have the same vertical position withrespect to, e.g., absorption grating 123 or any other optical componentof X-ray interferometer 100. Correspondingly, dashed line 204Arepresents a first set of image data, and dashed line 204B represents asecond set of image data for a selected horizontal cross-section ofnon-magnified image 200A and magnified image 200B, respectively. Dashedlines 204A and 204B are at some instances hereinafter also referred toas first image data set 204A and second image data set 204B,respectively. Both first image data set 204A and second image data set204B are selected at identical positions of image matrix.

As can readily be seen from FIGS. 4A and 4B, apart from the differentlevel of noise, the respective phase contrast signal intensity of firstimage data set 204A is almost identical to phase contrast signalintensity of second image data set 204B, despite the magnification by Mequalling about 1.485.

In other words, the difference in the phase contrast signal intensitiesfor, e.g., M equalling about 1 and M equalling about 1.485 is negligiblysmall. It may follow from the aforesaid that even for significantmagnification by, for example, about 150%, the phase contrast signalintensity of the magnified image remains substantially unchanged.

In FIGS. 4A and 4B, the horizontal axis X (position coordinate denoted“X_(object)/mm”), which represents a lateral position along the field ofview, was scaled such that the profiles of the plastic rods match theirthickness or width in the image plane (approx. 6 mm). The vertical axis,which represents the amplitude of the differential phase contrastsignal, is non-scaled to the height of the plastics in the image plane.

Performance Comparison Regarding Magnification M and Phase ContrastSensitivity S

Tables 1 to 4 compare X-ray interferometer 100 configurations againstconventional X-ray interferometers. The parameters outlined hereinregarding X-ray interferometer 100 are by no means to be construed aslimiting and thus do not limit the scope of what is disclosed herein.

For all setups exemplified below in the Tables 1 to 4 below, thefollowing parameters may apply:

-   -   L_(tot) equalling about 1.5 m, which denotes the distance from        the focal spot of X-ray source 110 to sensor plane of detector        140,    -   Operating energy of the source substantially equals about 20        keV, and    -   the Fractional Talbot order is n=4.

Furthermore, for the conventional approach it is assumed that the totallength of the setup obeys L_(tot)=I+d.

The phase contrast sensitivity S, measured in [rad⁻¹], may bedetermined, for example, as outlined by T. Donath, M. Chabior, F.Pfeiffer, 0. Bunk, E. Reznikova, J, Mohr, E, Hempel, S, Popescu, M,Hoheisel, M, Schuster, J. Baumann, and C. David, in “Inverse geometryfor grating-based x-ray phase-contrast imaging”, J. Appl. Phys. 106,054703 (2009).

In the conventional X-ray interferometers exemplified herein below, thegratings are relatively close to detector 140, e.g. absorption grating123 is directly in front of detector 140. Therefore, the grating area ofabsorption grating 123 is required to substantially cover the entiresensor field of detector 140, whereas for X-ray interferometer 100, therequired area of absorption grating 123 scales with the magnificationfactor M when compared to the area of the field of view of detector 140.

In the examples outlined below with respect to Table 1 and Table 2 it isassumed that the distance between the gratings is identical (e.g., about10 cm):

TABLE 1 Comparison setup I (Magnification M equals about 5): P₁₂₂ P₁₂₃ Id d_(s) S [μm] [μm] [cm] [cm] [cm] d_(M) [cm] [rad⁻¹] Conventional 3.413.65 140.0 10.0 110 0 59 X-ray interferometer X-ray 3.0 3.96 30.0 10.0 0110 = 253 interferometer (140 − 30) 100

TABLE 2 Comparison setup II - Magnification M equals about 10: P₁₂₂ P₁₂₃I d d_(s) S [μm] [μm] [cm] [cm] [cm] d_(M) [cm] [rad⁻¹] Conventional3.41 3.65 140.0 10.0 125 0 29 X-ray interferometer X-ray 2.73 4.55 15.010.0 0 125 = 220 interferometer (150 − 100 15 − 10)

The grating periods P₁₂₂ and P₁₂₃ are of the same order of magnitude forboth the conventional X-ray interferometer and X-ray interferometer 100.However, the phase contrast sensitivity is considerably higher for X-rayinterferometer 100 than for the conventional X-ray interferometer by,for example, a multiplicative factor ranging, for example, from about1.1 to about 10 or higher. An increase in the multiplicative factor ofthe phase contrast sensitivity may be, for example, about at least 1.2,about at least 1.3, about at least 1.5, about at least 2, about at least1.5, about at least 3.5, about at least 4, about at least 5, about atleast 6, about at least 7, about at least 7.5, about at least 8, aboutat least 9 or about at least 10. Phase contrast sensitivities that maybe attainable with X-ray interferometer 100 may be for example, rangefrom about 150 to about at least 300 and, for example, attain values ofabout at least 160, about at least 170, about at least 180, about atleast 190 at about least at least 200, about at least 210, about atleast 220, about at least 230, about at least 240, about at least 250,about at least 260, about at least 270, about at least 280 or about atleast 290.

Referring now to Tables 3 and 4, grating period P₁₂₂ was adjusted suchthat the sensitivity S becomes substantially equal for both theconventional X-ray interferometer and X-ray interferometer 100.Furthermore, for X-ray interferometer 100 parameter P₁₂₂ was set asabout 3 μm, which may then define the other parameters for X-rayinterferometer 100.

TABLE 3 Comparison III - Magnification M equals about 5 P₁₂₂ P₁₂₃ I dd_(S) S [μm] [μm] [cm] [cm] [cm] d_(M) [cm] [rad⁻¹] Conventional X- 6.815.1 67.5 82.5 37.5 0 242 ray interferometer X-ray 3.0 3.96 30.0 10.0 0110 242 interferometer 100

TABLE 4 Comparison IV - Magnification M equals about 10 P₁₂₂ P₁₂₃ I dd_(M) S [μm] [μm] [cm] [cm] d_(S) [cm] [cm] [rad⁻¹] Conventional X- 5.1430.0 26.0 124.0 11 0 242 ray interferometer X-ray 3.0 5.8 15.0 14.0 0121 242 interferometer 100As can readily be derived from the data in Table 3 and Table 4, theattained phase contrast sensitivity is the same for M equalling about 5and M equalling about 10 for both the conventional X-ray interferometerand X-ray interferometer 100. Although for the conventional X-rayinterferometer, object 130 is positioned such that d_(s)>0,substantially the same phase contrast sensitivity is attained by X-rayinterferometer 100, where object 130 is positioned directly in front ofphase grating 122 (d_(s) substantially equals 0). This is because thegrating periods P₁₂₂ and P₁₂₃ of the conventional X-ray interferometerare considerably larger than in X-ray interferometer 100, which offsetsany loss in phase contrast sensitivity which would otherwise occur fords>0 and for d_(M) that substantially equals 0.

In embodiments, grating periods for P₁₂₂ and P₁₂₃ in X-rayinterferometer 100 may be substantially smaller than in known phasegrating imaging systems where d_(M) equals about 0. Its width cantherefore be smaller sized than those of substantially non-magnifyingX-ray interferometer. For example, P₁₂₂ and P₁₂₃ may be equal or lessthan about 6 μm, 5 μm, 4 μm, or 3 μm, for d_(M)>0 and, optionally, whend_(s) is as small as possible. As a consequence, X-ray interferometer100 may be relatively compact in size. Moreover, since a change in themultiplicative factor M may be attained by altering d_(M) instead ofd_(s), it is not required that X-ray interferometer 100 based on, e.g.,Talbot grating interferometer, features a large distance d between thegratings in order to achieve the magnification. In embodiments, thedistance between phase grating 122 and absorption grating 123 in X-rayinterferometer 100 may be less than half of the total setup lengthL_(tot).

Any of the above-outlined embodiments, examples and implementations ofX-ray interferometer 100 are applicable in conjunction with dark-fieldX-ray imaging.

In terms of visible-light Fourier optics, dark-field illuminationremoves the zeroth order (unscattered light) from the diffractionpattern formed at the rear focal plane of the objective lens forobtaining an image that is formed exclusively from higher-anglediffraction intensities scattered by the specimen. Quite similarly, whenemploying, according to embodiments, dark-field illumination with X-rayinterferometer 100, information about the scattering power of object 130is contained in the higher order of the intensity oscillation respectiveof each pixel of detector 140. The intensity oscillation is responsiveto angle scattering in object 130 which might occur as a consequence ofmicro-structuring of object 130. X-ray interferometer 100 can thusprovide images representing X-ray angle scattering that might be causedby object 130. Microstructures may for example be attributed to porosityof at least some of object 130.

In some embodiments, phase contrast imaging system may also provide aconventional X-ray attenuation image.

In the discussion unless otherwise stated, terms such as“substantially”, “at least approximately” and “about” modifying acondition or relationship characteristic of a feature or features of anembodiment of the invention, are understood to mean that the conditionor characteristic is defined to within tolerances that are acceptablefor operation of the embodiment for an application for which it isintended.

It should be understood that an embodiment is an example orimplementation of embodiments. The various appearances of “oneembodiment,” “an embodiment” or “some embodiments” do not necessarilyall refer to the same embodiments.

Although various features may be described in the context of a singleembodiment, the features may also be provided separately or in anysuitable combination. Conversely, features may be described herein inthe context of separate embodiments for clarity, these features may alsobe implemented in a single embodiment.

Reference in the specification to “one embodiment”, “an embodiment”,“some embodiments” or “other embodiments” means that a particularfeature, structure, or characteristic described in connection with theembodiments is included in at least one embodiment, but not necessarilyall embodiments. It should be understood that the phraseology andterminology employed herein is not to be construed as limiting and isfor descriptive purpose only.

The principles and uses of the teachings of the embodiments may bebetter understood with reference to the accompanying description,figures and examples. It should be understood that the details set forthherein do not construe a limitation to an application of the disclosedembodiments. Furthermore, it should be understood that the embodimentscan be carried out or practiced in various ways and that the systemand/or method can be implemented with embodiments other than the onesoutlined in the description herein.

It should be understood that the terms “including”, “comprising”,“consisting” and grammatical variants thereof do not preclude theaddition of one or more components, features, steps, integers or groupsthereof.

The meaning of “in” includes “in” and “on”. The term “based” on is notexclusive and provides for being based on additional factors notdescribed, unless otherwise indicated.

If the specification or claims refer to “an additional” element, thatdoes not preclude there being more than one of the additional element.

It should be understood that where the claims or specification refer to“a” or “an” element, such reference is not to be construed as therebeing only one of that element.

It should be understood that where the specification states that acomponent, feature, structure, or characteristic “may”, “might”, “can”or “could” be included, that particular component, feature, structure,or characteristic is not required to be included.

The term “method” and “process” refers to manners, means, techniques andprocedures for accomplishing a given task including, but is not limitedto those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the art to which the disclosed system and methodbelong.

The descriptions, examples, methods and materials presented in theclaims and the specification are not to be construed as limiting butrather as illustrative only.

The disclosed embodiments can be implemented in the testing or practicewith methods and materials equivalent or similar to those describedherein.

It should be noted that the discussion that values or measures disclosedherein above should by no means to be construed as limiting and are forexemplary purposes only.

Descriptions of embodiments in the present application are provided byway of example and are not intended to limit the scope of theembodiments. The described embodiments comprise different features, notall of which are required in all embodiments. Some embodiments utilizeonly some of the features or possible combinations of the features.Variations of embodiments that are described, and embodiments comprisingdifferent combinations of features noted in the disclosure, will occurto persons of the art.

What is claimed is:
 1. An X-ray interferometer for imaging an object byirradiating the object with X-ray emitted at a given radiation energyfrom an X-ray source, comprising: a phase grating for phase-shiftingX-ray emanating from the object and which is incident onto the phasegrating; and an absorption grating for intensity modulating thephase-shifted X-ray; wherein the grating period of at least one of thephase grating and of the absorption grating are dimensioned such that anX-ray detector for imaging the object can be placed at a relativelylarge distance away from the absorption grating such that for the givenradiation energy, the X-ray flux incident onto the detector issubstantially non-adversely affected.
 2. The X-ray interferometeraccording to claim 1, wherein the grating period of the phase gratingand the grating period of the absorption grating are dimensioned suchthat the phase contrast sensitivity of the image of the object detectedby the detector is non-adversely affected.
 3. The X-ray interferometeraccording to claim 1, implemented as a Talbot-Lau interferometer.
 4. TheX-ray interferometer according to claim 1, implemented as a Talbotinterferometer.
 5. The X-ray interferometer according to claim 1,operative at a fractional Talbot order of n=4.
 6. The X-rayinterferometer according to claim 1, wherein the lateral extensions ofthe phase grating, the absorption grating and the detector aredimensioned such to cover the diverging field size respective of theX-ray emanating from the imaged object.
 7. The X-ray interferometeraccording to claim 1, wherein, during imaging, the distance between theobject and the phase grating substantially equals zero.
 8. The X-rayinterferometer according to claim 1, wherein the lateral dimensions ofthe phase grating and the absorption grating are such to allow forselecting the distance between the detector and the absorption gratingto obtain, when imaging the object, a corresponding change in themultiplicative factor between the lateral dimensions of the image of theobject and the object itself.
 9. The X-ray interferometer according toclaim 7, wherein the multiplicative factor ranges from 1 to about atleast
 50. 10. The X-ray interferometer according to claim 1, wherein thegrating period of the phase grating is equal or less than about 5 μm.11. The X-ray interferometer according to claim 1, wherein the gratingperiod of the absorption grating is equal or less than about 5 μm. 12.The X-ray interferometer according to claim 1, wherein the distancebetween the absorption grating and the detector ranges from about 5 cmto about at least 2 meters.
 13. The X-ray interferometer according toclaim 1, wherein the phase contrast sensitivity of the obtainable imageof the object ranges from about 150 to about at least
 300. 14. The X-rayinterferometer according to claim 1, wherein the gratings periods of theabsorption and phase grating are dimensioned such that distance betweenthe phase grating and absorption grating is small compared to thedistance between the detector and the absorption grating and thedistance between the source and the phase grating.
 15. The X-rayinterferometer according to claim 1, wherein the lateral extensions ofthe phase grating, the absorption grating and the detector aredimensioned such to cover the diverging field size respective of theX-ray emanating from the imaged object and wherein, during imaging, thedistance between the object and the phase grating substantially equalszero.
 16. The X-ray interferometer according to claim 1, wherein thephase contrast sensitivity of the obtainable image of the object rangesfrom about 150 to about at least 300, and wherein the gratings periodsof the absorption and phase grating are dimensioned such that distancebetween the phase grating and absorption grating is small compared tothe distance between the detector and the absorption grating and thedistance between the source and the phase grating.
 17. The X-rayinterferometer according to claim 1, wherein the gratings periods of theabsorption and phase grating are dimensioned such that distance betweenthe phase grating and absorption grating is small compared to thedistance between the detector and the absorption grating and thedistance between the source and the phase grating, and wherein, duringimaging, the distance between the object and the phase gratingsubstantially equals zero.
 18. A method for performing phase contrastimaging by employing an X-ray interferometer that is operative toirradiate an object with X-ray at a given radiation energy, the X-rayinterferometer comprising: a phase grating for phase-shifting X-rayemanating from the object and incident onto the phase grating; and anabsorption grating for intensity modulating the phase-shifted X-ray; themethod comprising the following procedure: placing an X-ray detector ata relatively large distance away from the absorption grating.
 19. Themethod according to claim 18, wherein the method comprises positioningthe object at distance from the phase grating which substantially equalszero.
 20. The method according to claim 18 comprising: dark-fieldilluminating the object for obtaining a dark-field image thereof.